Estimation of the shortest service life of SPD power supply lightning protection device
SPD power supply lightning protection device, since it is installed in the power system, how long can it be used effectively for at least 10 years? 20 years? This is one of the concerns of every customer.
The shortest service life of an SPD power lightning arrester is related to the basic quality of the varistor used, the number of varistors contained in the SPD, the number of lightning strikes, the harsh conditions of use, and the level of ambient temperature.
Qualitative analysis of the basic quality of the varistor is poor. A set of SPD contains a large number of varistors, a large number of lightning strikes, harsh use conditions (such as installation in a strong shock and vibration environment) and high ambient temperature, and the service life of the SPD is reduced.
1) Boundary conditions
1.1 The service life of a single varistor described in “GJBZ 299C-2006 Electronic Equipment Reliability Prediction Manual” under normal conditions is 1/9*10-8 hours, which is about 1000 years;
1.2 According to the requirements of “GB 18802.1-2011 Low Voltage Surge Protector (SPD) Part 1 Protector Performance Requirements and Test Methods for Low Voltage Distribution Systems”, each polarity of the power supply SPD can withstand the lightning impact of the rated state 15 A total of 30 times for positive and negative polarity;
1.3 The average trouble-free working time of common electronic circuits is 10000h (hours). About 1.12a.
2)Probability of lightning strikes per year for various types of buildings
It is required by “GB50057-2010 Building Lightning Protection Design Code”,
Number of lightning strikes for the second type of lightning protection structure
Provincial and ministerial-level office buildings are expected to have more than 0.06 lightning strikes/a;
The expected number of lightning strikes for general civil buildings is greater than 0.3 times/a;
Number of lightning strikes for the third type of lightning protection structures
The estimated number of lightning strikes for provincial and ministerial office buildings is 0.012 times/a~0.06 times/a;
The expected number of lightning strikes for general civil buildings is 0.06 times/a~0.3 times/a.
3) The commonly used power supply SPD is composed of 3 modules, each module can install at most 2 varistor lightning protection components, a total of 8 varistors form a set of SPD.
4) It can be calculated from the above boundary conditions
The service life of a power supply SPD is calculated based on the number of lightning strikes that can withstand 30 times, and the service life is:
Among them: K confidence coefficient 0.8
N Varistor withstands the minimum number of rated currents
P Probability of the maximum number of lightning strikes to the building 0.3 times/a
Maximum number of varistors installed in M 1 set of SPD
Power SPD Lightning resistance service life 0.8* 30 times/0.3 times a year/8 pieces=10 (years)
Taking into account that the average trouble-free working time of other electronic systems of SPD (such as remote signaling and temperature insurance) is not less than 10000h (hours) about 1.14 years.
On the basis of checking the use status of the SPD once a year, the minimum reliable service life of the SPD is not less than 10 years.
In high temperature environments and areas with frequent lightning strikes, the minimum reliable service life of SPD is not less than 5 years.